Overview
Definition:
A below-knee popliteal artery aneurysm (BKPAA) is a localized, irreversible dilation of the popliteal artery segment distal to the knee joint
It is defined as a diameter greater than 1.5 times that of the adjacent proximal artery or exceeding 10 mm
These aneurysms are the most common peripheral arterial aneurysms, predominantly affecting men and often associated with systemic atherosclerotic disease.
Epidemiology:
BKPAAs account for approximately 70% of all peripheral arterial aneurysms and 4% of all arterial aneurysms
They occur most frequently in men over 60 years old, with a male-to-female ratio of 10:1
Approximately 50% of patients with BKPAA also have an abdominal aortic aneurysm (AAA)
Bilateral BKPAAs are present in about 40-50% of cases.
Clinical Significance:
BKPAAs pose a significant risk of complications, including thrombosis, distal embolization leading to acute limb ischemia, rupture, and nerve compression
Early diagnosis and appropriate management are crucial to prevent limb loss and mortality
Understanding the surgical exposure and exclusion techniques is vital for vascular surgery residents preparing for DNB and NEET SS examinations.
Clinical Presentation
Symptoms:
Often asymptomatic, detected incidentally on imaging
Palpable pulsatile mass behind the knee
Pain in the calf or foot
Symptoms of acute limb ischemia from thrombosis or embolization: sudden onset of severe pain, pallor, pulselessness, paresthesia, paralysis, poikilothermia
Swelling or a feeling of fullness in the popliteal fossa.
Signs:
A pulsatile, expansile mass in the popliteal fossa, often best appreciated with the knee in slight flexion
A palpable thrill or audible bruit may be present
Signs of acute limb ischemia if embolization or thrombosis has occurred: decreased or absent distal pulses, cool skin, sensory deficits, motor weakness, cyanosis
Signs of nerve compression: foot drop or calf pain due to sciatic nerve involvement.
Diagnostic Criteria:
Diagnosis is typically confirmed by imaging
A diameter of the popliteal artery exceeding 10 mm or more than 1.5 times the diameter of the adjacent superior popliteal artery is diagnostic
Presence of a pulsatile mass on physical examination in a patient with risk factors for atherosclerosis.
Diagnostic Approach
History Taking:
Inquire about symptoms suggestive of limb ischemia: sudden onset of calf pain, numbness, tingling, weakness, or coldness
Ask about the presence of a pulsatile mass
Assess for cardiovascular risk factors: hypertension, hyperlipidemia, diabetes mellitus, smoking history
Ask about prior vascular interventions or known aneurysms elsewhere
Screen for bilateral BKPAAs and abdominal aortic aneurysms.
Physical Examination:
Carefully palpate the popliteal fossa for a pulsatile mass, noting its size, expansile nature, and tenderness
Assess distal pulses (dorsalis pedis, posterior tibial) and assess for presence of bruits over the mass
Examine the entire limb for signs of ischemia: skin temperature, color, capillary refill, sensation, and motor function
Examine the contralateral limb and palpate the abdomen for an AAA.
Investigations:
Duplex ultrasonography: Primary imaging modality for diagnosis, assessing aneurysm diameter, length, thrombus burden, and flow dynamics
Provides information on patency of distal vessels
Computed tomography angiography (CTA): Gold standard for detailed anatomical assessment, evaluating extent of aneurysm, involvement of trifurcation, and suitability for endovascular repair
Magnetic resonance angiography (MRA): Alternative to CTA, particularly useful in patients with contrast allergies or renal insufficiency
Conventional angiography: Primarily used for planning endovascular interventions, less common for initial diagnosis.
Differential Diagnosis:
Baker's cyst: Palpable mass behind the knee, but typically not pulsatile and lacks a thrill/bruit
Popliteal vein aneurysm: Rare, may present as a compressible mass
Arterial pseudoaneurysm: History of trauma or prior arterial puncture
Lymphadenopathy: Usually firm, non-pulsatile
Ganglion cyst: Common benign cyst, firm and immobile.
Management
Indications For Intervention:
Symptomatic aneurysms (acute limb ischemia, rupture, nerve compression)
Asymptomatic aneurysms with a diameter > 2.0 cm
Rapidly expanding aneurysms (> 5 mm in 6 months)
Presence of mural thrombus that may embolize
Patients with a life expectancy of > 2 years.
Surgical Management Open Repair:
Procedure involves incision in the popliteal fossa, dissection of the aneurysm sac, ligation of feeding arteries proximally and distally, and interposition graft (synthetic or autologous vein)
Techniques include ligation and bypass, or direct sac excision and reconstruction
Management of distal arterial occlusive disease is often addressed simultaneously.
Endovascular Management:
Exclusion of the aneurysm using stent grafts, typically deployed from the adductor canal proximally to the tibioperoneal trunk distally
Indications include patients unfit for open surgery, complex anatomy, or as a primary approach
Requires suitable proximal and distal landing zones
Coil embolization is an option for very small or inaccessible aneurysms.
Postoperative Care:
Close monitoring for signs of limb ischemia, graft occlusion, or endoleak
Routine duplex ultrasound surveillance is essential to assess graft patency and detect complications
Management of pain, anticoagulation (if indicated), and ambulation
Long-term risk factor modification (smoking cessation, blood pressure control, statin therapy).
Complications
Early Complications:
Graft thrombosis
Distal embolization causing acute limb ischemia
Wound infection
Nerve injury (e.g., foot drop)
Hemorrhage
Endoleak (in endovascular repair).
Late Complications:
Graft occlusion
Pseudoaneurysm formation
Graft infection
Stenosis at anastomosis or within the graft
Distal embolization from graft thrombus
Aneurysm rupture (rare after successful repair).
Prevention Strategies:
Meticulous surgical technique
Adequate inflow and outflow assessment
Appropriate graft material selection
Careful preoperative planning for both open and endovascular approaches
Strict adherence to postoperative surveillance protocols
Aggressive management of atherosclerotic risk factors.
Prognosis
Factors Affecting Prognosis:
Presence and severity of limb ischemia at presentation
Adequacy of distal revascularization
Graft patency
Presence of comorbidities
Patient's life expectancy
Successful exclusion of the aneurysm.
Outcomes:
Open surgical repair has excellent long-term limb salvage rates, typically > 90%
Endovascular repair offers good short- to mid-term outcomes but may have higher rates of reintervention or failure compared to open repair, particularly in the long term
Rupture is associated with high mortality.
Follow Up:
Lifelong surveillance is recommended
For open repair, annual clinical examination and duplex ultrasound are standard
For endovascular repair, more frequent imaging surveillance (e.g., 6 months, 1 year, then annually) is crucial to monitor for endoleaks, graft migration, and occlusion
Patients require ongoing management of vascular risk factors.
Key Points
Exam Focus:
BKPAAs are the most common peripheral aneurysms
High association with AAA and bilateral involvement
Major complications are thrombosis and embolization leading to acute limb ischemia
Management options include open repair (ligation-bypass) and endovascular exclusion.
Clinical Pearls:
Always palpate the popliteal fossae bilaterally and assess distal pulses in patients with peripheral vascular disease or AAA
Suspect BKPAA in any patient presenting with acute calf pain or a pulsatile mass behind the knee
CTA is crucial for planning endovascular repair, evaluating landing zones.
Common Mistakes:
Missing bilateral aneurysms
Underestimating the risk of embolization in thrombosed aneurysms
Inadequate distal assessment during open repair
Insufficient surveillance after endovascular repair leading to missed endoleaks or graft occlusion
Incorrect patient selection for endovascular therapy.